Chemical milling method and bath for steel

ABSTRACT

Chemical milling of stainless steel and high nickel alloys by immersing the same in a bath of 3 to 15 percent by volume sulphuric acid, 3 to 15 percent hydrochloric acid, 2 to 6 percent nitric acid, 0.1 to 5 percent lignin, more particularly a vegetable tannin, as an inhibitor, and remainder water; and maintaining the steel or alloy in the bath at such temperature and for such time as to remove a desired quantity of metal. A best combination of results is had with the extract of the bark of Acacia Mollissima serving as the inhibitor. In milling martensitic and ferritic stainless steel, the bath additionally may contain phosphoric acid. And in milling austenitic stainless steel, the bath additionally may contain hydrofluoric acid.

AU 165 EX United States Patent Kreml [54] CHEMICAL MILLING METHOD AND BATH FOR STEEL John F. Kreml, Phoenix, Md.

Armco Steel Corporation, Middletown, Ohio July 1, 1969 Inventor:

Assignee:

Filed:

Appl. No.:

References Cited UNITED STATES PATENTS Swihart ..2s2/79.4 x

IlI IIIIIII-IlIllIllllI ill/l ill 3,349,037 10/1967 Peterson ..252/79.4 X

Primary Examiner-Jacob H. Steinberg Attorney-John Howard Joynt [5 7] ABSTRACT Chemical milling of stainless steel and high nickel alloys by immlllfllbfijminjjalh 0f 3 to 15 percent by volume s ulp h u r ig acid,3 to 15. percent hydrochloric acid, 2 to 6 per.- ce nt ni tr ic acid, 0. l to 5 percent Iignin m re particularlya, vegetable tannin, as an inhibitor, and remainder water and maintaining the steel or alloy in the bath at such temperature and for such time as to remove a desired quantity of metal. A best combination of results is had with the extract of the bark of Acacia Mollissima sewing as the inhibitor. In milling martensitic and ferritic stainless steel, the bath additionally may contain phosphoric acid. And in milling austgnitic stainless steel, the bath additionally may contain hydrofluoric acid.

12 Claims, No Drawings PKTENTEDwm 1912 INVENTOR I John E Krem/ J2 7!. 2% BY fir; ATTORNEY CHEMICAL MILLING METHOD AND BATH FOR STEEL As a matter of introduction, an object of my invention is the provision of a safe, effective and comparatively inexpensive method for chemically milling or removing metal from the surface of stainless steel and high nickel alloys.

Another object is the provision of a method for removing metal from the surface of stainless steel bar, rod, wire and other metal stock in such simple, direct and reliable manner as to either eliminate seams, fissures or other surface discontinuities or to so modify the same as to permit correction by subsequent mechanical processing, and yet give a dull finish which lends itself to the application of lead or other lubricant for further processing as by cold-drawing.

Another object is the provision of a bath for removing metal from stainless steel, whether it be of the ferritic, martensitic or austenitic grade, with maximum life of bath and minimum fuming while in use of while merely standing.

Other objects of my invention in part will be readily apparent and in part more particularly pointed to in the description which follows.

The invention, therefore, consists in the combination of ingredients and mixtures of materials and in the several steps and the relation of each of the same to one or more of the others as more fully described herein, the scope of the application of which is indicated in the claims at the end of this specification.

BACKGROUND OF THE INVENTION As an aid to better understanding of my invention, it may be well to note at this point that at this date the stainless steels are well established in the art. The number of different grades is legion. All of these steels contain chromium in substantial amount, this ranging from about percent to about 35 percent. Many of the straight-chromium grades are ferritic, with carbon in low amount, that is, 0.08 percent max., or even better, carbon not exceeding 0.05 percent. The ferritic grades are not hardenable by heat-treatment.

Others of the straight-chromium grades are martensitic, essentially containing chromium as noted, along with a necessary carbon content, that is, 0.10 percent or 0.12 percent up to 0.25 percent or more. The martensitic grade is hardenable by heat-treatment.

Perhaps the widest variety of grades essentially contains nickel in large amount, say 7 percent to 35 percent or more, along with chromium, these steels being austenitic, nonhardenable by heat-treatment, ductile, and readily formable. Many of these steels, however, may be hardened by coldwork.

In more recent years, there have been developed agehardening or precipitation-hardening grades of stainless steel, some being martensitic as hardened and others being austenitic, this depending upon composition. All contain chromium in the amount of some 10 percent to 35 percent, with nickel in the amount of some 3 percent to 30 percent, and generally with one or more of the ingredients titanium, copper, and aluminum to effect precipitation-hardening.

Now in many industrial applications stainless steel, whether of the ferritic, the martensitic, or the austenitic type, and especially in the precipitation-hardening grades which are austenitic or martensitic, high surface quality is essential. For example, in the aircraft and space industries there are required bolts, screws, rivets and other fasteners possessing great strength at elevated temperatures. These conveniently may be fashioned from cold-heading wire or the grade A 286 (about percent chromium, about 28 percent nickel, about 2 percent titanium, and remainder iron). The steel is comparatively ductile and forrnable in the annealed condition. And subsequent to forming, as by cold-heading, threading and the like, the formed products are hardened through precipitation heat-treatment.

In producing the various fasteners for the aircraft and space industries, it is essential that cold-heading wire be absolutely free of surface defects, for otherwise a seam or other discontinuity on the surface of the metal opens and shows up as a crack in the forming operation. And in general, the higher the strength the greater the damage from cracks, seams or other surface defects. These fasteners, therefore, are customarily made from cold-heading wire that has been shaved or turned to remove all surface defects. But I find that the turning is inclined to give a barber-pole" efiect, a defect in itself. And even with the shaving, any defect in the shaving tool may introduce a discontinuity of its own. In either event, the shaving, turning or the like is an expensive operation and tends to smear over or obscure the defects.

While metal may be removed from the surface of stainless steel by other known methods, such as an electro-polishing operation (for example, the method described and claimed in the Ostrofsky U.S. Pat. No. 2,335,354 of Nov. 30, 1943 or the method for polishing stainless steel without benefit of electrolytic treatment in accordance with the teaching of the Hayes and Lamokin U.S. Pat. No. 2,694,001 of Nov. 9, 1954 and that of the Swihart U.S. Pat. No. 2,662,814 of Dec. 15, 1953), all processes are rather costly. In the first, the require ment for electrolytic treatment necessitates special electrolytic apparatus and special handling. Moreover, the steel is given an undesired polished surface which! find does not readily accept leading" or other treatment with lubricant for subsequent processing. In the others, best results necessitate the use of the inhibitor quinoidine, an ingredient of significant cost and one not readily available. And here again, the inclination is to polish rather than eliminate metal with resultant graying or micro-roughening of the surface.

Accordingly, one of the objects of my invention is the provision of a simple, inexpensive and thoroughly practical method of removing metal from the surface of stainless steel and high nickel alloys, as for example in producing stainless steel and nickel alloy wire suited to the production of cold-headed and other fasteners, which steel or alloy is essentially free of surface defect or blemish which would result in a crack in the surface of the metal, and which is characterized by a microroughness and freedom from polish.

SUMMARY OF THE INVENTION Turning now more especially to the practice of my invention, I provide what I term a chemical milling operation for stainless steel and the high nickel alloys in which the steel or alloy, conveniently in the form of wire, is treated in a bath of particular composition, preferably at particular temperature and for particular period of time, to uniformly and effectively remove a significant portion of the metal itself. I find that in the practice of my process the metal at the base of a crack is somewhat protected by gas evolution. By progressive treatment, however, especially where the metal is intermittently removed from the bath and gas evolution interrupted, the cracks become more shallow and less sharp. In a subsequent drawing operation the metal pops out, or up as the case may be, and there is had a surface virtually free of crack or discontinuity. The surface, however, is not bright or highly polished, but rather is dull and well adapted to accept a lubricant for subsequent processing, as in cold-drawing the metal.

While the process of my invention may be practiced on a single filament of wire passed through the treating bath of my invention, for reasons of economy I prefer a batch operation in which successive coils of wire are immersed within the bath for desired period of time.

Now the bath itself conveniently is made up and held in a wooden tank or vat. Conveniently, the contents of the vat, that is, the chemical milling solution, is heated by live steam passed into the solution by way of a flexible hose with pipe outlet manipulated by an operator. In general, the bath is brought to a temperature of about F. to about F. for use.-l find that the reaction between the bath and metal is exothennic, the heat thus developed generally offsetting the heat losses from the surface of the bath to maintain the desired operating temperature.

The bath of my invention essentially consists of about 3 percent to about 15 percent by volume sulphuric acid, about 3 percent to about 15 percent hydrochloric acid, about 2 percent to about 6 percent nitric acid, about 0.1 percent to about percent lignin as an inhibitor, with remainder water. By reference to lignin" I intend to embrace lignose and lignone. Particularly good results are had where it is a vegetable tannin that is employed as the inhibitor. A best combination of results in terms of uniformity of metal removal, desired dull surface, long life of bath, and minimum foaming, spray and odor is had by employing the vegetable tannin comprising distillation residue or extract of the bark of Acacia Mollissima, a tree common to South Africa (see Chemistry of Leather," Vol. 2, edited by OFlaherty, et al., Reinhold Publishing Corporation, New York, 1958, notably pages 111, 125-126 and 164). In my bath the lignin addition not only serves as an inhibitor to excessive attack, but also serves to provide a foam blanket which masks the bath, retains heat, keeps spray and odors down, and prevents evaporation. Actually, I feel that the foam blanket partially may be attributed to cellulose coming from the wood of the tank itself. l find, contrary to results had with certain prior baths, that the bath of my invention leaves no film on the treated metal which in prior practices results in a burning or oxidation of the metal surface during a subsequent annealing operation. With my treatment there is had a clean, uniform surface characterized by a micro-roughness, as above indicated, which well serves to retain lead or other lubricant applied for a wire-drawing operation.

As a further feature, I find that the bath of my invention, when its activity becomes slowed with use, may be revitalized by spiking with hydrochloric and nitric acids, each in amount somewhat short of the original additions. Actually, the life of the bath is significantly better than the baths of the prior art where it is quinoidine which is employed as an inhibitor.

While l am not certain of the point, and prefer not to be bound by explanation, it is my view that with the bath of my invention the lignin inhibitor serves to assure a cleansing of the seams and surface discontinuities of the metal being treated, this by permitting the formation of minute gas bubbles which rise from the base of the seam or discontinuity and eliminate any wax, oil or the like deriving from prior processing, foreign substances which are inclined to preclude proper metal removal and seam elimination.

BRIEF DESCRIPTION OF THE DRAWING in the chemical milling method and bath of my invention, 1 conveniently employ apparatus and equipment illustratively shown in the accompanying drawing in elevation view with cenain parts being shown in section to better show others.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrative of the practice of my invention, the coils of stainless steel wire to be treated 10 (see the accompanying drawing) are hung on a yoke 11 from an overhead crane (not shown) and opened up by hand to give free access to the solution 12 contained in vat 13 as noted above. The coils are immersed in the vat of hot solution, initially heated by live steam supplied by hose 14, for a period of some 4 or 5 minutes, after which they are withdrawn from the bath, measured, moved about on the yoke, and again immersed in the bath for further metal removal. I find that best results are had where the total amount of metal removed is on the order of 0.005 inch, this from the diameter of wire of some to 56-inch diameter. In general, the total time of treatment in the bath ranges from about 5 minutes to 30 minutes, the length of time in a measure depending upon the grade of stainless steel being treated, the composition of the particular bath, the bath temperature, and, to some extent, the age of the bath. Usually there are required three or four immersions with intermediate withdrawals and measurement of diameter to achieve the desired removal of metal, this to the extent of taking 0.005 inch off the diameter as noted. And, as noted, with each withdrawal of the work from the bath the strands of wire are moved about by hand in order to safely assure access of the bath to all parts of the wire.

When it appears that the desired amount of metal has been removed from the wire, the coils are washed down with water under pressure and set aside for drying and subsequent leading, oxide-coating, copper-coating, liming or other conditioning prior to cold-drawing. The surface of the metal is desirably dull, for l find that the bright, shiny, highly polished surface which characterizes the electro-polished stainless steel is not suited to subsequent leading and cold-drawing.

While in the chemical milling of stainless steel of most grades, as well as the high nickel alloys, I employ an immersion bath or solution essentially consisting of about 3 percent to about 15 percent by volume sulphuric acid, about 3 percent to about 15 percent hydrochloric acid, about 2 percent to about 6 percent nitric acid, about 0.1 percent to about 5 percent lignin, notably the extract of Acacia Mollissima bark, with remainder water, as described above, for certain particular grades of steel or nickel alloys I employ an immersion bath of more limited and special composition, i.e., about 5 percent to about 12 percent sulphuric acid, about 5 percent to about 12 percent hydrochloric acid, about 2 percent to about 4 percent nitric acid, about 1 percent to about 3 percent extract of the bark of Acacia Mollissima, and remainder water. For the chemical milling of the martensitic and ferritic stainless steels, that is, the steels which essentially are the straight-chromium grade with or without small additions of nickel, molybdenum, and the like, I employ a bath essentially consisting of about 10 percent by volume sulphuric acid, about 10 percent hydrochloric acid, about 3 percent nitric acid, about 2 percent extract of the bark of Acacia Mollissima, with remainder water. Such a bath not only is highly effective to give desired metal removal, but is found to have a comparatively long, useful life, that is, a life of many hours. During treatment, the bath usually is maintained at a temperature of some to F. for a best combination of unifonnity of treatment and efi'iciency.

Better results are had in the ferritic and martensitic stainless steels, however, particularly the AIS] Types 410 (l 1.5 13.5 percent chromium, 0.15 percent max. carbon, and remainder iron) and 431 (15 17 percent chromium, 1.25 2.50 percent nickel, 0.20 percent max. carbon, and remainder iron), as well as the precipitation-hardening grade Armco 17-4 PH 17 percent chromium, 4 percent nickel, 4 percent copper, 0.07 percent max. carbon, and remainder iron), where there is employed an immersion bath essentially. consisting of about 7 percent by volume sulphuric acid, about 7 percent hydrochloric acid, about 3 percent nitric acid, with about 2 percent extract of the bark of Acacia Mollissima, and the remainder water. i find that with this bath there is less tendency for the metal to pit, particularly with over-exposure, a somewhat undesirable attribute of the 10-10-3 bath described immediately above. With the 7-7-3 bath the temperature of treatment is on the order of some 175 to 185 F., although the broader range of 175 to F. may be employed where desired.

For the ferritic, martensitic and precipitation'hardening grades of stainless steel, best results are had with an immersion bath essentially consisting of about 7 percent by volume sulphuric acid, 7 percent hydrochloric acid, 2 percent nitric acid, with about 2 percent of the extract of the bark of Acacia Mollissima, and the remainder water. This bath gives best results with a minimum of fuming. Here the bath temperature is maintained at about 175 F.

Excellent results in treating the martensitic and ferritic stainless steels, as well as the precipitation'hardening grades, are had with an immersion bath essentially consisting of about 5 percent by volume sulphuric acid, about 5 percent hydrochloric acid, about 4 percent nitric acid, about 4 percent phosphoric acid, about 2 percent extract of the bark of Acacia Mollissima, and remainder water. Here again, the bath preferably is maintained at about 175 to 185 F. during treatment of the steel. This bath is particularly efi'ective for the precipitation-hardening stainless steels Armco 17-4 PH, and

the Armco PH 13-8 Mo (13 percent chromium, 8 percent nickel, 2.5 percent molybdenum, 0.05 percent max. carbon, and remainder iron). As well, the solution is highly effective on the A181 Types 410 and 431 and the further AISl Types 420 (12-14 percent chromium, carbon exceeding 0.15 percent, and remainder iron), 440 (16-18 percent chromium, 0.60-1.20 percent carbon, and remainder iron) and 446 (23-27 percent chromium, 0.20 percent max. carbon, 0.25 percent max. nitrogen, and remainder iron). ln treating the precipitation-hardening grades of stainless steel best results, with freedom from intergranular attack, are achieved by treating the steels in the annealed or solution-treated condition, that is, following heating at some l,600 to 2,150" F.

For the austenitic stainless steels, that is, the A181 300 series, the A-286 and other high nickel alloys, a somewhat different composition is employed for best results. For, in general, it may be said that the austenitic chromium-nickel stainless steels, as well as the high nickel alloys, are more acidresistant than the straight-chromium grades. Best results are had with an immersion bath essentially consisting of about 5 percent by volume sulphuric acid, about 5 percent hydrochloric acid, about 4 percent nitfigacid, about 4 percent hydrofluoric acid, with about 2 percent extract of Acacia Mollissima bark, and remainder water. And in the practice of the method of my invention in connection with the austenitic alloys I prefer to maintain the bath at a temperature of about 180 to 190 F. Here again, the time of treatment may range from some 5 minutes to 30 minutes.

In conclusion, it will be seen that I provide in my invention a chemical milling process and immersion bath in which the various objects hereinbefore set forth and the many advantages thereof are successfully achieved.

In its specific aspects, as well as its broadest aspects, the chemical milling process of my invention effectively removes the desired quantity of the surface metal without at the same time resulting in objectionable intergranular attack, pitting, or other undesired local action. Metal removal is uniform throughout. The immersion bath is prepared from the comparatively inexpensive and readily-available materials sulphuric acid, hydrochloric acid, nitric acid, and the available lignin inhibitor, particularly a vegetable tannin. The immersion bath is comparatively safe, with freedom from objectionable odor when not in use, and with a minimum of noxious or other fumes when in operation.

Since many embodiments may be made of my invention, and since many changes and variations may be made in the embodiments set out above, it is to be understood that all matter described herein is to be interpreted as being illustrative, and not by way of limitation.

lclaim:

l. The art of treating stainless steel and nickel alloys which comprises immersing the same for such time, in an aqueous bath comprising about 3 percent to about percent by volume sulphuric acid, about 3 percent to about 15 percent hydrochloric acid, about 2 percent to about 6 percent nitric acid, and about 0.1 percent to about 5 percent extract of Acacia Mollissima bark, maintained at such temperature, as to remove a desired quantity of metal and give a microroughened surface with minimum discontinuity and pitting.

2. In the chemical milling of martensitic and ferritic stainless steels, the art which comprises immersing the steel in a bath essentially consisting of about 10 percent by volume sulphuric acid, about 10 percent hydrochloric acid, about 3 percent nitric acid, about 2 percent extract of Acacia Mollissima bark, and remainder water; and maintaining said steel in said bath at such temperature and for such time as to remove a hydrochloric acid, about 2 percent to about 3 percent nitric acid, about 2 percent extract of Acacia Mollissima bark, and

remainder water; and maintaining said steel in said bath at such temperature and for such time as to remove a desired quantity of metal and give a micro-roughened surface with minimum discontinuity and pitting.

4. ln the chemical milling of martensitic, ferritic and precipitation-hardenable stainless steels, the art which comprises immersing the steel in a bath essentially consisting of about 5 percent by volume sulphuric acid, about 5 percent hydrochloric acid, about 4 percent nitric acid, about 4 percent phosphoric acid, about 2 percent extract of Acacia Mollissima bark, and remainder water; and maintaining said steel in said bath at such temperature and for such period of time as to remove a desired quantity of metal and give a microroughened surface with minimum discontinuity and pitting.

5. In the chemical milling of the austenitic stainless steels and nickel alloys, the art which comprises immersing the steel or alloy in a bath essentially consisting of about 5 percent by volume sulphuric acid, about 5 percent hydrochloric acid, about 4 percent nitric acid, about 4 percent hydrofluoric acid, about 2 percent extract of Acacia Mollissima bark, and remainder water; and maintaining said steel or alloy in said bath at such temperature for such time as to remove a desired quantity of metal and give a micro-roughened surface with minimum discontinuity and pitting.

6. Chemical milling according to claim 1 wherein the aqueous bath is contained in a wooden tank or vat.

7. Chemical milling according to claim 1 in which steel or alloy wire coil is maintained in the bath, with at least one intermediate withdrawal and moving about, at a temperature of to F. for a total period of about 4 minutes to 30 minutes.

8. Chemical milling of martensitic and ferritic stainless steels according to claim 1 wherein the bath essentially consists of about 5 percent to about 12 percent sulphuric acid by volume, about 5 percent to about 12 percent hydrochloric acid, about 2 percent to about 4 percent nitric acid, about 1 percent to about 3 percent extract of Acacia Mollissima bark, and remainder water.

9. Chemical milling bath essentially consisting of about 3 percent to about 15 percent by volume sulphuric acid, about 3 percent to about 15 percent hydrochloric acid, about 2 percent to about 6 percent nitric acid, about 0.1 percent to about 5 percent extract of Acacia Millissima bark, and remainder water.

10. Bath according to claim 9 essentially consisting of about 7 percent by volume sulphuric acid, about 7 percent hydrochloric acid, about 2 percent nitric acid, about 2 percent extract of Acacia Millissima bark, and remainder water.

11. Chemical milling bath essentially consisting of about 5 percent by volume sulphuric acid, about 5 percent hydrochloric acid, about 4 percent nitric acid, about 4 percent hydrofluoric acid, about 2 percent extract of Acacia Mollissima bark, and remainder water.

12. Chemical milling bath essentially consisting of about 5 percent by volume sulphuric acid, about 5 percent hydrochloric acid, about 4 percent nitric acid, about 4 percent phosphoric acid, about 1 percent to about 3 percent extract of Acacia Mollissima bark, and remainder water.

i t 1% i 

2. In the chemical milling of martensitic and ferritic stainless steels, the art which comprises immersing the steel in a bath essentially consisting of about 10 percent by volume sulphuric acid, about 10 percent hydrochloric acid, about 3 percent nitric acid, about 2 percent extract of Acacia Mollissima bark, and remainder water; and maintaining said steel in said bath at such temperature and for such time as to remove a desired quantity of metal and give a micro-roughened surface with minimum discontinuity and pitting.
 3. In the chemical milling of martensitic, ferritic and precipitation-hardenable stainless steels, the art which comprises immersing the steel in a bath essentially consisting of about 7 percent by volume sulphuric acid, about 7 percent hydrochloric acid, about 2 percent to about 3 percent nitric acid, about 2 percent extract of Acacia Mollissima bark, and remainder water; and maintaining said steel in said bath at such temperature and for such time as to remove a desired quantity of metal and give a micro-roughened surface with minimum discontinuity and pitting.
 4. In the chemical milling of martensitic, ferritic and precipitation-hardenable stainless steels, the art which comprises immersing the steel in a bath essentially consisting of about 5 percent by volume sulphuric acid, about 5 percent hydrochloric acid, about 4 percent nitric acid, about 4 percent phosphoric acid, about 2 percent extract of Acacia Mollissima bark, and rEmainder water; and maintaining said steel in said bath at such temperature and for such period of time as to remove a desired quantity of metal and give a micro-roughened surface with minimum discontinuity and pitting.
 5. In the chemical milling of the austenitic stainless steels and nickel alloys, the art which comprises immersing the steel or alloy in a bath essentially consisting of about 5 percent by volume sulphuric acid, about 5 percent hydrochloric acid, about 4 percent nitric acid, about 4 percent hydrofluoric acid, about 2 percent extract of Acacia Mollissima bark, and remainder water; and maintaining said steel or alloy in said bath at such temperature for such time as to remove a desired quantity of metal and give a micro-roughened surface with minimum discontinuity and pitting.
 6. Chemical milling according to claim 1 wherein the aqueous bath is contained in a wooden tank or vat.
 7. Chemical milling according to claim 1 in which steel or alloy wire coil is maintained in the bath, with at least one intermediate withdrawal and moving about, at a temperature of 175* to 195* F. for a total period of about 4 minutes to 30 minutes.
 8. Chemical milling of martensitic and ferritic stainless steels according to claim 1 wherein the bath essentially consists of about 5 percent to about 12 percent sulphuric acid by volume, about 5 percent to about 12 percent hydrochloric acid, about 2 percent to about 4 percent nitric acid, about 1 percent to about 3 percent extract of Acacia Mollissima bark, and remainder water.
 9. Chemical milling bath essentially consisting of about 3 percent to about 15 percent by volume sulphuric acid, about 3 percent to about 15 percent hydrochloric acid, about 2 percent to about 6 percent nitric acid, about 0.1 percent to about 5 percent extract of Acacia Millissima bark, and remainder water.
 10. Bath according to claim 9 essentially consisting of about 7 percent by volume sulphuric acid, about 7 percent hydrochloric acid, about 2 percent nitric acid, about 2 percent extract of Acacia Millissima bark, and remainder water.
 11. Chemical milling bath essentially consisting of about 5 percent by volume sulphuric acid, about 5 percent hydrochloric acid, about 4 percent nitric acid, about 4 percent hydrofluoric acid, about 2 percent extract of Acacia Mollissima bark, and remainder water.
 12. Chemical milling bath essentially consisting of about 5 percent by volume sulphuric acid, about 5 percent hydrochloric acid, about 4 percent nitric acid, about 4 percent phosphoric acid, about 1 percent to about 3 percent extract of Acacia Mollissima bark, and remainder water. 